Decline in serum tryptase levels in response to imatinib mesylate therapy. Serum tryptase levels before and after imatinib mesylate therapy are shown as a function of time for 6 patients with MHES and elevated serum tryptase levels. The normal range for serum tryptase levels (≤ 11.5 ng/mL) is indicated by the shaded box. Serum tryptase levels for all patients declined rapidly to normal levels and remained in the normal range throughout therapy.